The collection of waste fluids in sewers has promoted and expanded urbanized industrial society by permitting increasingly larger collections of people to live within close proximity of one another. Conventionally, sewage and waste fluids are transported from a residential or commercial structure into the city's sewer network via gravity flow, usually by locating the sewer main further beneath ground surface than the sewage effluent lines of the structures that feed it. Where the land surface topography makes this impossible, a lift station or the equivalent must be added within the network to generate a flow-inducing hydraulic gradient. Once in the sewer network, the waste fluid is transported through increasingly larger sewer mains to an outflow location, typically a wastewater treatment facility. While such a system provides a simple and efficient method of removing waste fluids from the structures of an urban community, the necessity of open lines in a gravity-driven flow network creates the possibility of sewage back flow. That is, under certain conditions, the sewage flow direction can be reversed, causing sewage to flow from the sewer main into the structures intended to feed it, resulting in the deposition of sewage and waste fluids within the lower levels of residential homes and commercial buildings. Such an occurrence often results in significant property damage and may additionally pose a serious human health hazard. Consequently, devices have been designed to allow flow directed from the structure to the city sewer, but to prevent return flow from the sewer main into the structure.
Most commonly, such devices are employed during periods of heavy rain, because most municipalities do not maintain separate storm and sanitary sewer lines. Thus stormwater runoff is often channeled through the sanitary sewer lines. During heavy periods of rain, stormwater runoff accumulates upon surfaces, such as parking lots and roadways, through which it cannot infiltrate. These surfaces are often designed to channel runoff into a gutter leading to entryways into the city's sewer network. Stormwater runoff additionally enters the sewer main through the manholes that allow repair technician access. If sufficient in intensity and duration, heavy rains can result in the influx of fluids into the sewer network that is greater than the maximum flowrate capacity of the sewer mains. The fluid level in the sewer main then rises, potentially up to street level via the manhole access risers. Once the fluid level in the sewer network elevates above the sewage effluent lines of the structures that feed it, the hydraulic gradient reverses and gravity forces fluid to flow from the sewer main into the feed lines.
As stated above, various types of sewage back flow prevention devices have been created to guard against such occurrences. One common solution involves the installation of a one-way valve or flap within the structure sewage effluent line. An example is shown in U.S. Pat. No. 5,234,018, issued to Grachal et al. The Grachal et al. device uses a hinged flap that seats against a lip on the structure sewage effluent line. During normal operation, the pressure of the gravity-driven sewage outflow against the flap causes it to swivel to an open position, allowing the outflow to enter the sewer main. However, when the hydraulic gradient reverses and the sewage flow direction changes, the flap is forced against the lip of the structure effluent line, which prevents it from swiveling and effectively seals the structure off from the sewer network. Unfortunately, however, this type of device often becomes clogged with debris and/or sewage deposits and fails to seal properly when the flow reverses, thereby permitting passage of waste fluid back into the feed line. Furthermore, this type of device cannot be manually actuated, and instead only becomes functional by the action of the sewage back flow itself.
Another method conventionally used to prevent sewage back flow involves the installation of a valve between the structure sewage effluent pipe and the sewer main. An example is shown in U.S. Pat. No. 5,775,365, issued to Hayden et al. The Hayden et al. device includes the use of a ball valve between the sewer main and the structure sewage effluent line. By closing the valve, the structure's sewage line can be sealed from the rest of the sewer network, preventing waste fluid from entering the structure. Unlike the hinged flap, this type of device may be used anticipatorily. That is, the structure may be manually sealed from the sewer main at any time in anticipation of actual sewage back flow. However, this type of device likewise suffers from the same disadvantage that it may be rendered ineffective if the junction to the valve becomes clogged with debris and/or sewage deposits and fails to close properly, thereby permitting passage of waste fluid into the structure.
There is a need for a device which can be used anticipatorily to prevent the back flow of waste fluid from a sewer main into a structure, and can seal the structure from the sewer network even if debris and/or sewage deposits have accumulated in the system.